This invention relates to a gear-within-gear pump and more particularly to such a gear-within-gear fuel pump for automotive fuel systems or the like.
Heretofore, gear-within-gear fuel pumps, generally similar to that shown in FIGS. 1-4 of the drawings herein, were on sale and in public use more than one year prior to the filing date of the instant application. However, it was found that the pumping elements (i.e., the gear-within-gear pumping elements and the motor) grew progressively more noisy as the pumping elements became worn. Since many of these fuel pumps are utilized in electronic fuel injection systems for relatively expensive cars, and since oftentimes the fuel pump will operate for some short time prior to starting the engine of the car, automobile manufacturers and automobile owners were sensitive to the noise generated by such fuel pumps.
It has been found that a certain portion of the noise generated by such fuel pumps is caused because excessive tolerances between the effective diameters of the external and internal gears, and because of the necessary spaces between the outer periphery of the internal gear and the inner wall of the eccentric ring which receives the internal gear.
During testing of such gear-within-gear fuel pumps, the pumping elements were found to become more noisy and they "wore in". It was also found that tolerances between the external and internal gear and between the outer surface of the eccentric ring and the pump housing tended to change which, in turn, decreased the compression ratio of the pump and increased pump friction. In addition to increasing the noise levels of the pump, such changes in dimensions adversely affected the flow capacity and efficiency of the pump.